The Bush administration is coming under renewed attack over whether its claim that Iraq possessed weapons of mass destruction was backed up by solid evidence. A group of private American weapons experts is now calling for an independent commission to look into the matter. But the Bush administration continues to defend its pre-war claims, which were the basis for military action against Iraq.

The Carnegie Endowment for International Peace is charging that in the days before the war, the Bush administration misrepresented the threat from Iraq by saying it possessed weapons of mass destruction and was ready to use them.

Jessica Mathews, president of the Washington-based research group, points to a speech last February that Secretary of State Colin Powell made to the U.N. Security Council and televised around the world.

"He went out of his way to emphasize our certainty, saying, 'every statement I make today is backed up by solid sources,'" said Ms. Mathews, quoting Colin Powell. "'These are not assertions. We are giving you facts and conclusions based on solid evidence. This is evidence not conjecture, this is true.' And yet we know that a great many of the major assertions made in that speech turned out not to be true."

During a news conference Thursday, the secretary of state stood by the evidence, saying Iraq did have dangerous weapons and the United States was justified in ousting Saddam Hussein. "I knew exactly the circumstances under which I was presenting that speech to the U.N. on the 5th of February," said Mr. Powell. "Anything that we did not feel was solid and multi-sourced, we did not use in that speech."

He has not changed his view that Iraq - which had used banned weapons on its own people, as well as during the country's war with Iran during the 1980s - intended to use them again if the allies had not acted.

"Where the debate is, is why haven't we found huge stockpiles and why haven't we found large caches of these weapons," said the secretary. "Let's let the Iraqi survey group complete its work. There has been the movement out of some of the individuals from the group. I presume that their particular job is finished. But I am confident of what I presented last year."

But he is less certain than others in the Bush administration that Saddam Hussein had ties to terrorist groups like al-Qaida. "I have not seen 'smoking gun'-concrete evidence about the connection," he said, "but I think the possibility of such connections did exist and it was prudent to consider them."

Before the war, some in the Bush administration including Defense Secretary Donald Rumsfeld had cited what they called 'bulletproof' evidence of Iraqi ties to a group linked to Osama bin Laden's al-Qaida terrorist network.